Road vehicle tires are usually produced by superimposing a number of layers of elastomeric material defining at least two multilayer annular products, respectively consisting of an inner carcass and an outer tread belt.
The outer tread belt includes an outer tread band surrounding a reinforcing belt having at least one tread ply, while the inner carcass usually has a substantially U-shaped section, and includes an annular layer defined by a body ply and by an innerliner covering a part of the inner surface of the body ply, the remaining inner surface of which is covered by two abrasion strips and two sidewalls on opposite sides of the innerliner. The carcass also includes two beads, each housed inside a respective lateral wall of the carcass formed by turning a respective lateral end of the annular layer up and about or around the bead.
For achieving maximum uniformity of the tire, the above two multilayer intermediate products and, especially, those produced by combining the same, i.e. the finished or assembled green tires, are generally compacted by means of a stitching operation.
The following description deals solely, though without departing from the wider scope of the present invention, with the stitching together of said two multilayer intermediate products for producing a finished green tire, no mention being made of any intermediate stitching for compacting each of said two multilayer intermediate products, to which the same considerations also apply.
For producing a finished green tire, the outer tread belt is normally stitched onto the inner carcass from the outside. In order to withstand this stitching process the green tire must be connected in a fluid-tight manner to an inner support and be properly inflated. Moreover, to enable it to be stitched from the outside, the outer surface of the green tire must be freely accessible. External stitching is usually performed by rotating the green tire in contact with a stationary stitching device as a result of which a given, usually radial, pressure is applied onto the tire.
A major drawback of external stitching is that, due to the freedom of movement of the outer surface of the green tire, any distortion of the tire caused by the radial pressure applied by the stationary stitching device is totally uncontrollable, and may easily result in displacement of the cords in the body plies and/or tread plies, thus seriously impairing the uniformity of the tire. Moreover, when applied externally, said radial pressure may result in failure of the joining or adhesion of the innerliner relative to the carcass.